Bioelectrical impedance measuring device and measuring method

Abstract

To provide a measuring device and a measuring method of bioelectric impedance capable of measuring impedance inside a living body without depending on a degree of dryness of a skin surface.SOLUTION: A measuring device 100 includes a first electrode pair (111 and 112), a second electrode pair (121 and 122), a third electrode pair (131 and 132), a current source 140, a voltmeter 160, a negative impedance transformation circuit 170, and a calculation part 190. The negative impedance transformation circuit 170 generates impedance of the skin of a living body, and feeds it back to the voltmeter 160. The calculation part 190 calculates impedance of a muscle of the living body on the basis of a voltage of the voltmeter 160 and a current flowing through the current source 140.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technical field of the present specification relates to a device and method for measuring bioelectrical impedance, and in particular to measuring impedance inside a living body. [Background technology]

[0002] A method for assessing muscle mass and water content by passing an electric current through a living body and measuring bioelectrical impedance is known. Bioelectrical impedance is studied in the medical field because it is simple and non-invasive.

[0003] For example, Patent Document 1 discloses a technique for measuring bioelectrical impedance using a four-electrode method. Patent Document 1 also discloses a technique for determining bioelectrical impedance using an impedance model that takes into account skin resistance Rs, fat resistance Rf, extracellular fluid resistance Re, intracellular fluid resistance Ri, and bone resistance Rb.

[0004] Patent Document 2 discloses a technique for measuring the common mode voltage of a coated cable by using a common mode voltage measuring device, and also discloses a technique for using a negative impedance conversion circuit (NIC) as a compensation circuit for compensating for the parasitic capacitance component that occurs between a measurement electrode and a conductor. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2007-521102 [Patent Document 2] Japanese Patent Publication No. 2020-30165 Summary of the Invention [Problem to be solved by the invention]

[0006] To measure the impedance of a living body with high accuracy, it is necessary to consider the contribution of the impedance of each part of the body. Among the parts of the body, the impedance of the skin has a large absolute value. Furthermore, the impedance of the skin varies greatly depending on the dryness. For example, when a person sweats due to exercise, the impedance varies greatly. For this reason, it is difficult to measure the impedance of muscles inside the living body with high accuracy.

[0007] The problem to be solved by the technology of this specification is to provide a bioelectrical impedance measuring device and a measuring method that can measure the impedance inside a living body without depending on the degree of dryness of the skin surface. [Means for solving the problem]

[0008] The bioelectrical impedance measuring device in the first aspect includes a first pair of electrodes to be brought into contact with a living body, and a second pair of electrodes to be brought into contact with the living body; a third electrode pair for contacting the living body; The device includes a current source that applies a current between a first electrode pair, a voltmeter that measures the voltage between a second electrode pair, a negative impedance conversion circuit connected between the voltmeter and one terminal of the second electrode pair, and a calculation unit. The second electrode pair is brought into contact with a position inside the contact position between the living body and the first electrode pair. The third electrode pair is brought into contact with the second electrode pair adjacent to a position inside the contact position between the living body and the first electrode pair. The negative impedance conversion circuit is The positive and negative values ​​of the real and imaginary parts of the impedance between the third electrode pair are inverted to obtain a negative impedance. As it generates , negative impedance is The impedance of the skin of a living body To cancel it out The signal is fed back to the voltmeter. The calculation unit calculates the impedance of the muscle of the living body based on the voltage of the voltmeter and the current flowing through the current source.

[0009] This bioelectrical impedance measuring device includes a negative impedance conversion circuit that outputs a negative impedance, allowing the bioelectrical impedance measuring device to derive muscle impedance without relying on skin impedance, which is susceptible to change due to dryness. [Effects of the Invention]

[0010] This specification provides a bioelectrical impedance measuring device and a measuring method that can measure the impedance inside a living body regardless of the degree of dryness of the skin surface. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram showing the configuration of a bioelectrical impedance measuring device 100 according to a first embodiment. [Figure 2] FIG. 1 is a diagram conceptually showing impedance inside a living body. [Figure 3] FIG. 1 is a diagram showing the configuration of a conventional bioelectrical impedance measuring device using a four-electrode method. [Figure 4] 4 is a diagram showing an equivalent circuit of the bioelectrical impedance measuring device according to the four-electrode method of FIG. 3. FIG. [Figure 5] This is an equivalent circuit drawn by extracting the skin impedance Zs and the muscle impedance Zm. [Figure 6] FIG. 6 is a diagram in which the notation of skin impedance Zs is changed from that of FIG. 5. [Figure 7] 10 is a graph showing frequency characteristics of the real part of the impedance Zs of the skin. [Figure 8] 10 is a graph showing the frequency characteristics of the imaginary part of the impedance Zs of the skin. [Figure 9] This is a circuit for calculating bioelectrical impedance when the negative impedance conversion circuit 170 is not used. [Figure 10] 10 is a graph showing the simulation results of bioelectrical impedance when the simulation circuit of FIG. 9 is used. [Figure 11] 10 is a simulation circuit showing the bioelectrical impedance Z1a when the negative impedance conversion circuit 170 is not used. [Figure 12] 1 is a simulation circuit showing a negative impedance conversion circuit 170. [Figure 13]10 is a simulation circuit showing a method for measuring bioelectrical impedance Z2 when a negative impedance conversion circuit 170 is used. [Figure 14] 12 is a graph showing bioelectrical impedance Z1a when the simulation circuit of FIG. 11 is used. [Figure 15] 13 is a graph showing bioelectrical impedance Z1b when the simulation circuit of FIG. 12 is used. [Figure 16] 14 is a graph showing bioelectrical impedance Z2 when the simulation circuit of FIG. 13 is used. [Figure 17] 10 is a simulation circuit showing a method for measuring bioelectrical impedance in accordance with a measurement system when a negative impedance conversion circuit 170 is used. [Figure 18] 18 is a graph showing the simulation results of bioelectrical impedance when the simulation circuit of FIG. 17 is used. [Figure 19] FIG. 2 is a diagram showing the configuration of a bioelectrical impedance measuring device 200 according to a modified example of the first embodiment. [Figure 20] FIG. 2 is a diagram showing the configuration of a bioelectrical impedance measuring device 300 in a modified example of the first embodiment. [Figure 21] FIG. 10 is a diagram showing the configuration of a bioelectrical impedance measuring device 400 according to a modified example of the first embodiment. [Figure 22] FIG. 10 is a diagram showing the configuration of a bioelectrical impedance measuring device 500 according to a modified example of the first embodiment. [Figure 23] 10A and 10B are diagrams illustrating the operation of the bioelectrical impedance measuring device 500 according to a modified example of the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Specific embodiments will be described below using a bioelectrical impedance measurement device and measurement method as examples. However, the technology of this specification is not limited to these embodiments. In this specification, the term "living body" includes humans and other animals with skin and muscles, but does not include organisms without skin and muscles. Electrical information includes voltage, current, and impedance. The angle between two lines is defined as 0° to 90°. The line connecting the electrode terminals connects the center of gravity of the contact surface where one terminal contacts the living body and the center of gravity of the contact surface where the other terminal contacts the living body.

[0013] (First embodiment) 1. Measurement equipment 1 is a diagram showing the configuration of a bioelectrical impedance measuring device 100 according to a first embodiment. The measuring device 100 measures the internal impedance of a living body such as a human. The measuring device 100 includes a first electrode pair (111, 112), a second electrode pair (121, 122), a third electrode pair (131, 132), a current source 140, an ammeter 150, a voltmeter 160, a negative impedance conversion circuit 170, and a calculation unit 190. The ammeter 150 and the voltmeter 160 are measuring units for measuring impedance.

[0014] The first electrode pair (111, 112) has a first terminal 111 and a second terminal 112. The second electrode pair (121, 122) has a first terminal 121 and a second terminal 122. The third electrode pair (131, 132) has a first terminal 131 and a second terminal 132. Hereinafter, the notation in parentheses may be omitted for the first electrode pair (111, 112), the second electrode pair (121, 122), and the third electrode pair (131, 132).

[0015] The first terminal 111 and the second terminal 112 of the first electrode pair are electrodes for contacting the living body and for passing a current through the living body. The first terminal 111 and the second terminal 112 of the first electrode pair are arranged at predetermined positions on the living body, spaced apart from each other. The shape of the electrode terminals is, for example, circular. Alternatively, they may be rectangular, square, or other polygonal. The material of the electrodes is, for example, Au, Al, Cu, or Ag / AgCl.

[0016] The first terminal 121 and the second terminal 122 of the second electrode pair are electrodes for contacting the living body and for measuring the voltage applied to the living body. The first terminal 121 and the second terminal 122 of the second electrode pair are arranged at predetermined positions on the living body, spaced apart. The first terminal 121 and the second terminal 122 of the second electrode pair are arranged at a position that includes a straight line connecting the first terminal 111 and the second terminal 112 of the first electrode pair, and is between the contact position of the first terminal 111 and the contact position of the second terminal 112 of the first electrode pair. The shape and material of the electrode terminals of the second electrode pair are the same as those of the first electrode pair.

[0017] The first terminal 131 and the second terminal 132 of the third electrode pair are electrodes for contacting a living body and for measuring the impedance of the skin surface of the living body. The first terminal 131 and the second terminal 132 of the third electrode pair are arranged at predetermined positions on the living body, spaced apart. The first terminal 131 and the second terminal 132 of the third electrode pair are arranged at a position that includes a straight line connecting the first terminal 111 and the second terminal 112 of the first electrode pair, and is between the contact position of the first terminal 111 and the contact position of the second terminal 112 of the first electrode pair. The shape and material of the terminals of the electrodes of the third electrode pair are the same as those of the first electrode pair.

[0018] The current source 140 applies a current to the living body via the first electrode pair. In practice, the current source 140 applies a current between the first electrode pair. One terminal of the current source 140 is connected to the first terminal 111 of the first electrode pair, and the other terminal of the current source 140 is connected to the second terminal 112 of the first electrode pair. The current applied to the living body by the current source 140 is, for example, 500 μA or less. The frequency of the current applied by the current source 140 is, for example, 1 kHz or more and 1 MHz or less. The current source 140 has an ammeter 150 inside.

[0019] Ammeter 150 measures the value of current I1 flowing through the living body via first terminal 111 and second terminal 112 of the first electrode pair. Ammeter 150 measures the current flowing through current source 140. Current source 140 and ammeter 150 are connected to calculation unit 190.

[0020] Voltmeter 160 measures the voltage between first terminal 121 and second terminal 122 of the second electrode pair. One terminal of voltmeter 160 is connected to first terminal 121 of the second electrode pair, and the other terminal is connected to second terminal 122 of the second electrode pair via negative impedance conversion circuit 170. Voltmeter 160 is connected to calculation unit 190.

[0021] The negative impedance conversion circuit 170 generates an impedance corresponding to the impedance of the skin of a living body and feeds it back to a circuit including the voltmeter 160. The negative impedance conversion circuit 170 generates a skin impedance based on electrical information from the third electrode pair. Specifically, the negative impedance conversion circuit 170 inverts the impedance input from the third electrode pair and outputs the negative impedance to the circuit on the second electrode pair side. The negative impedance is obtained by inverting the positive and negative values ​​of the real and imaginary parts of the original impedance. The negative impedance conversion circuit 170 is connected to the circuit on the side of one terminal of the second electrode pair and to the circuit on the side of one terminal of the third electrode pair. The negative impedance conversion circuit 170 is connected between the voltmeter 160 and one terminal of the second electrode pair. The negative impedance conversion circuit 170 is connected to the calculation unit 190. The negative impedance conversion circuit 170 generates a skin impedance corresponding to the dry state. The skin impedance changes over time, for example, due to sweating.

[0022] The calculation unit 190 calculates the impedance of the muscle inside the living body based on the current value of the ammeter 150 and the voltage value of the voltmeter 160. The calculation unit 190 is connected to the ammeter 150, the voltmeter 160, and the negative impedance conversion circuit 170.

[0023] The angle formed by the line connecting first terminal 111 of the first electrode pair and second terminal 112 of the first electrode pair and the line connecting first terminal 121 of the second electrode pair and second terminal 122 of the second electrode pair is, for example, not less than 0° and not more than 10°. The angle formed by the line connecting first terminal 111 of the first electrode pair and second terminal 112 of the first electrode pair and the line connecting first terminal 131 of the third electrode pair and second terminal 132 of the third electrode pair is, for example, not less than 0° and not more than 10°.

[0024] The distance between first terminal 121 of the second electrode pair and first terminal 131 of the third electrode pair is, for example, not less than 0.1 mm and not more than 3 cm. The distance between second terminal 122 of the second electrode pair and second terminal 132 of the third electrode pair is, for example, not less than 0.1 mm and not more than 3 cm. The closer these distances are, the smaller the difference in dryness between the contact points of the terminals of the second electrode pair and the contact points of the terminals of the third electrode pair.

[0025] 2. Internal impedance of the living body FIG. 2 is a diagram conceptually illustrating the impedance inside a living body. As shown in FIG. 2, for example, in a human upper arm, there is a bone in the center, skeletal muscle around the bone, fat around the skeletal muscle, and skin around the fat. When measuring the impedance of a human body by contacting electrodes with the skin, the impedance of the skin Zs, the impedance of the fat Zf, and the impedance of the muscle Zm must be taken into consideration. Note that the impedance of the bone is sufficiently small compared to the impedance of the muscle, etc. Therefore, it is not necessary to take the impedance of the bone into consideration.

[0026] If the total impedance Za is measured by a voltmeter, the following equation holds: Za = 2·Zs + 2·Zf + Zm ………(1)

[0027] Here, the impedance Zf of fat is sufficiently smaller than the impedance Zs of skin, so an approximation can be made that drops the term for the impedance Zf of fat.

[0028] As will be described later, the measurement device 100 of the first embodiment measures the state of muscle fatigue of a living body. To do so, the measurement device 100 cancels the effect of the skin impedance Zs.

[0029] FIG. 3 is a diagram showing the configuration of a conventional bioelectrical impedance measuring device using the four-electrode method.

[0030] Figure 4 is a diagram showing the equivalent circuit of the bioelectrical impedance measuring device using the four-electrode method in Figure 3. Here, the skin impedances are Zs1a, Zs2a, Zs2b, and Zs1b, starting from the left side of Figure 4. The muscle impedances are Zm1a, Zm2, and Zm1b, starting from the left side of Figure 4. The internal resistance of the voltmeter is Rv, the internal resistance of an ideal voltmeter is infinity, the internal resistance of the ammeter is Ri, and the internal resistance of an ideal ammeter is 0.

[0031] To measure muscle impedance with high accuracy, the following two conditions must be met: |Zm2| << Rv ………(2) |Zs2a|< <Rv、|Zs2b|<<Rv ………(3)

[0032] In reality, the internal resistance of a voltmeter is finite, and as shown in Figure 4, a minute current I2 flows through the voltmeter.

[0033] Now, let's consider the case of a dry state. In a dry state, the absolute values ​​of the skin impedances Zs2a and Zs2b are large. Therefore, the above formula (3) does not necessarily hold. In this case, the relationship between the voltmeter measurement value V2 and the ammeter measurement value I1 is as follows: V2 / I2 = (V1-Vs2a-Vs2b) / I1 = V1 / I1 - (Vs2a+Vs2b) / I1 = Zm2 - (Zs2a+Zs2b) I2 / I1 ………(4)

[0034] The second term in equation (4) represents the measurement error. If the skin impedances Zs2a and Zs2b are excessively large even though the minute current I2 is small, the second term will take a large value.

[0035] Figure 5 shows an equivalent circuit that extracts the skin impedance Zs and muscle impedance Zm. The skin impedance Zs is expressed as a parallel circuit of the skin resistance Rs and skin capacitance Cs. The muscle impedance Zm is expressed as the intracellular fluid resistance Rin, the cell membrane capacitance Cmb, and the extracellular fluid resistance Rout. The intracellular fluid resistance Rin and the cell membrane capacitance Cmb are in series. The extracellular fluid resistance Rout is in parallel with the intracellular fluid resistance Rin and the cell membrane capacitance Cmb.

[0036] At this time, the impedance Zs of the skin is expressed by the following equation:

[0037]

number

[0038] Here, ω is the frequency and j is the imaginary unit. As shown in equation (5), the impedance Zs of the skin is expressed as the sum of the real part and the imaginary part.

[0039] FIG. 6 is a diagram in which the skin impedance Zs is shown in a different way from FIG.

[0040] Fig. 7 is a graph showing the frequency characteristics of the real part of the skin impedance Zs. As shown in Fig. 7, the drier the skin surface is, the larger the absolute value of the real part of the skin impedance Zs becomes.

[0041] Fig. 8 is a graph showing the frequency characteristics of the imaginary part of the skin impedance Zs. As shown in Fig. 8, the drier the skin surface is, the larger the absolute value of the imaginary part of the skin impedance Zs becomes.

[0042] Therefore, in order to eliminate the influence of the skin impedance Zs, it is necessary to consider both the absolute value of the real part and the absolute value of the imaginary part of the skin impedance Zs.

[0043] 3. Simulation (Simulation 1) 3-1.Simulation circuit 9 shows a circuit for calculating bioelectrical impedance without using the negative impedance conversion circuit 170. The impedance Zbi of the muscle is calculated from the voltage Vbi applied to the skeletal muscle and the current Ibi flowing through the circuit including the skeletal muscle.

[0044] In skeletal muscle, the cell membrane capacitance Cmb was 50 nF, the intracellular fluid resistance Rin was 20 Ω, and the extracellular fluid resistance Rout was 50 Ω. When the skin was wet, the skin resistance Rs was 1 kΩ and the skin capacitance Cs was 1 nF. When the skin was dry, the skin resistance Rs was 100 kΩ and the skin capacitance Cs was 1 nF. The internal impedance Rv of the voltmeter was 100 kV. The current frequency was varied within the range of 5 kHz to 100 kHz.

[0045] 3-2.Simulation results Fig. 10 is a graph showing the simulation results of bioelectrical impedance when using the simulation circuit of Fig. 9. The horizontal axis of Fig. 10 represents the real part of bioelectrical impedance Zbi, and the vertical axis of Fig. 10 represents the imaginary part of bioelectrical impedance Zbi.

[0046] When the skin is wet, the bioelectrical impedance Zbi traces a locus close to a circular arc in the fourth quadrant. When the skin is dry, the bioelectrical impedance Zbi moves from the first quadrant to the fourth quadrant while tracing a locus close to a circular arc.

[0047] Furthermore, the higher the frequency of the current passed through the living body, the smaller the difference between the bioelectrical impedance Zbi when the skin is wet and the bioelectrical impedance Zbi when the skin is dry.

[0048] 4. Negative Impedance Conversion Circuit (Simulation 2) 4-1.Simulation circuit In order to reduce the influence of the difference in bioelectrical impedance between wet and dry skin, the measuring device 100 includes a negative impedance conversion circuit 170 .

[0049] FIG. 11 is a simulation circuit showing the bioelectrical impedance Z1a when the negative impedance conversion circuit 170 is not used.

[0050] FIG. 12 is a simulation circuit showing a negative impedance conversion circuit 170. The negative impedance conversion circuit 170 has an inverting amplifier circuit using an operational amplifier OA1. The gain of the inverting amplifier circuit is −1. For example, it is assumed that the non-inverting input terminal of the operational amplifier OA1 is connected to the first terminal 131 of the third electrode pair, and the output terminal of the operational amplifier OA1 is connected to the second terminal 132 of the third electrode pair. Note that the first terminal 131 and the second terminal 132 may be reversed.

[0051] The negative impedance conversion circuit 170 generates a voltage waveform that is the inverse of the voltage input from the terminal corresponding to the third electrode pair. The impedance Z1c measured by the third electrode pair is approximately equal to the impedance Z1a measured by the second electrode pair. In the simulation, Z1a = Z1c.

[0052] 13 is a simulation circuit showing a method for measuring bioelectrical impedance Z2 when using negative impedance conversion circuit 170. Negative impedance conversion circuit 170 is disposed between second terminal 122 of the second electrode pair and voltmeter 160.

[0053] 4-2.Simulation results Figure 14 is a graph showing bioelectrical impedance Z1a when using the simulation circuit of Figure 11. The horizontal axis of Figure 14 represents frequency, and the vertical axis represents impedance. As shown in Figure 14, the absolute value of the real part of bioelectrical impedance Z1a decreases as frequency increases. The absolute value of the imaginary part of bioelectrical impedance Z1a decreases as frequency increases.

[0054] Fig. 15 is a graph showing bioelectrical impedance Z1b when using the simulation circuit of Fig. 12. As shown in Fig. 15, the absolute value of the real part of bioelectrical impedance Z1b decreases as the frequency increases. The absolute value of the imaginary part of bioelectrical impedance Z1b also decreases as the frequency increases.

[0055] The real part of bioelectrical impedance Z1b in Fig. 15 is close to the value obtained by inverting the positive and negative of the real part of bioelectrical impedance Z1a in Fig. 14. The imaginary part of bioelectrical impedance Z1b in Fig. 15 is close to the value obtained by inverting the positive and negative of the imaginary part of bioelectrical impedance Z1a in Fig. 14.

[0056] Fig. 16 is a graph showing bioelectrical impedance Z2 when the simulation circuit of Fig. 13 is used, where Z2 = Z1a + Z1b.

[0057] The absolute value of the real part of bioelectrical impedance Z2 is smaller than the absolute values ​​of the real parts of bioelectrical impedances Z1a and Z1b. The absolute value of the imaginary part of bioelectrical impedance Z2 is smaller than the absolute values ​​of the imaginary parts of bioelectrical impedances Z1a and Z1b. This is because bioelectrical impedance Z1a and bioelectrical impedance Z1b cancel each other out.

[0058] Here, bioelectrical impedance Z1a is considered to be the impedance of dry skin, which is highly frequency-dependent, and bioelectrical impedance Z2 is considered to be the impedance of skeletal muscle.

[0059] 5. Simulation (Simulation 3) Figure 13 is not a simulation circuit based on an actual measurement system.

[0060] 5-1.Simulation circuit Fig. 17 is a simulation circuit showing a method for measuring bioelectrical impedance in accordance with a measurement system when using a negative impedance conversion circuit 170. Note that Fig. 17 shows the positions corresponding to each electrode.

[0061] 5-2.Simulation results Fig. 18 is a graph showing the simulation results of bioelectrical impedance when the simulation circuit of Fig. 17 is used. Fig. 18 shows the results when the negative impedance conversion circuit 170 (NIC) is used and the results of Fig. 10.

[0062] 18, the bioelectrical impedance when the skin is dry when the negative impedance conversion circuit 170 (NIC) is used is approximately equal to the bioelectrical impedance when the skin is wet when the negative impedance conversion circuit 170 (NIC) is not used. Furthermore, even when a current with a relatively low frequency of about 5 kHz is used, the muscle impedance can be measured with high accuracy.

[0063] 5-3.Effects of negative impedance conversion circuit In this way, by using the negative impedance conversion circuit 170 (NIC), it is possible to measure the muscle impedance while eliminating the influence of the skin surface impedance, which changes significantly depending on whether the skin is wet or dry.

[0064] 6. Bioelectrical Impedance Measurement Method For example, first terminal 111 of the first electrode pair is brought into contact with the shoulder side of a person's upper arm, and second terminal 112 of the first electrode pair is brought into contact with the fingertip side of the upper arm. First terminal 121 and second terminal 122 of the second electrode pair are brought into contact with the person's upper arm at positions inside the contact points of first terminal 111 and second terminal 112 of the first electrode pair. First terminal 131 and second terminal 132 of the third electrode pair are brought into contact with the person's upper arm at positions inside the contact points of first terminal 111 and second terminal 112 of the first electrode pair.

[0065] Then, current source 140 passes a small current between first terminal 111 and second terminal 112 of the first electrode pair. In this state, voltmeter 160 measures the voltage applied between first terminal 121 and second terminal 122 of the second electrode pair. Negative impedance conversion circuit 170 generates a negative impedance by inverting the positive and negative of the impedance between the third electrode pair. Calculation unit 190 of measurement device 100 calculates the impedance of the muscles in the person's upper arm based on the negative impedance from negative impedance conversion circuit 170 and the impedance between the second electrode pair. At this time, negative impedance conversion circuit 170 cancels out the impedance of the skin.

[0066] 7. Effects of the First Embodiment The measuring device 100 of the first embodiment has a negative impedance conversion circuit 170 connected to a voltmeter 160. The negative impedance conversion circuit 170 generates a negative impedance by inverting the positive and negative of the voltage value input from the third electrode pair and inputs this to a circuit including the second electrode pair. This eliminates the influence of impedance that is highly variable depending on the dryness of the skin surface. Therefore, the measuring device 100 can measure the internal impedance of a living body with high accuracy, regardless of the dryness of the skin surface. Therefore, the measuring device 100 can evaluate the degree of muscle fatigue of a living body.

[0067] 8. Variations 8-1. Electrode position FIG. 19 is a diagram illustrating the configuration of a bioelectrical impedance measuring device 200 according to a modified example of the first embodiment. As illustrated in FIG. 19, the line connecting the first terminal 221 and the second terminal 222 of the second electrode pair may be different from the line connecting the first terminal 231 and the second terminal 232 of the third electrode pair. The second electrode pair and the third electrode pair are disposed inside the first terminal 111 and the second terminal 112 of the first electrode pair. The first terminal 221 of the second electrode pair and the first terminal 231 of the third electrode pair are adjacent to each other. The second terminal 222 of the second electrode pair and the second terminal 232 of the third electrode pair are adjacent to each other. The angle formed by the line connecting the first terminal 221 of the second electrode pair and the first terminal 231 of the third electrode pair and the line connecting the second terminal 222 of the second electrode pair and the second terminal 232 of the third electrode pair is, for example, between 0° and 30°.

[0068] 8-2.Resistance FIG. 20 is a diagram showing the configuration of a bioelectrical impedance measuring device 300 according to a modification of the first embodiment. As shown in FIG. 20, the measuring device 300 includes a resistor 381 connected between the first terminal 221 of the second electrode pair and the voltmeter 160, and a resistor 382 connected between the first terminal 231 of the third electrode pair and the negative impedance conversion circuit 170. The resistance values ​​of resistors 381 and 382 are different. For example, the resistance value of resistor 382 is greater than the resistance value of resistor 381. Because the resistances of resistors 381 and 382 are different, the magnitude relationship between the second electrode pair and the third electrode pair is maintained over time. Therefore, the negative impedance conversion circuit 170, which is a positive feedback circuit, operates stably.

[0069] 8-3. Electrode shape FIG. 21 is a diagram showing the configuration of a bioelectrical impedance measuring device 400 according to a modified example of the first embodiment. As shown in FIG. 21, the measuring device 400 has a comb-tooth-shaped first terminal 421 and a comb-tooth-shaped second terminal 422 of the second electrode pair, and a comb-tooth-shaped first terminal 431 and a comb-tooth-shaped second terminal 432 of the third electrode pair. The comb-tooth shape of the first terminal 421 of the second electrode pair and the comb-tooth shape of the first terminal 431 of the third electrode pair can be arranged in an interdigitated state. The comb-tooth shape of the second terminal 422 of the second electrode pair and the comb-tooth shape of the second terminal 432 of the third electrode pair can be arranged in an interdigitated state. Alternatively, the two terminals may be arranged so that one of the terminals interdigitates with the other.

[0070] 21, the extension direction of the comb teeth is perpendicular to the line connecting the first terminal 111 and the second terminal 112 of the first electrode pair. The extension direction of the comb teeth may be inclined within a range of 60° to 90° with respect to the line connecting the first terminal 111 and the second terminal 112 of the first electrode pair. The extension direction of the comb teeth may be parallel to the line connecting the first terminal 111 and the second terminal 112 of the first electrode pair.

[0071] 8-4. Switch 22 is a diagram showing the configuration of a bioelectrical impedance measuring device 500 according to a modification of the first embodiment. The measuring device 500 includes a switch SWB, a control unit Cnt1, an impedance storage unit Mem1, and a negative impedance conversion circuit 570. The measuring device 500 includes a first electrode pair and a first terminal 521 and a second terminal 522 of a second electrode pair.

[0072] The negative impedance conversion circuit 570 generates a waveform based on the waveform stored in the impedance storage unit Mem1. The impedance storage unit Mem1 stores the waveform that is the basis of the waveform generated by the negative impedance conversion circuit 570.

[0073] The control unit Cnt1 is connected to the switch SwB and the calculation unit 190. The switch SwB switches on and off the connection state between each terminal of the second electrode pair and each of the other units. The switch SwB has switches Sw1a, Sw1b, Sw2a, and Sw2b. The control unit Cnt1 controls the switches Sw1a, Sw1b, Sw2a, and Sw2b. The switch Sw1a switches on and off the connection between the first terminal 521 of the second electrode pair and the voltmeter 160. The switch Sw1b switches on and off the connection between the second terminal 522 of the second electrode pair and the negative impedance conversion circuit 570. The switch Sw2a switches on and off the connection between the first terminal 521 of the second electrode pair and the impedance memory unit Mem1. The switch Sw2b switches on and off the connection between the second terminal 522 of the second electrode pair and the impedance memory unit Mem1.

[0074] The control unit Cnt1 measures impedance using the second electrode pair during a first period and causes the negative impedance conversion circuit 570 to generate a negative impedance during a second period different from the first period. The control unit Cnt1 may alternately perform processing during the first period and processing during the second period. The impedance storage unit Mem1 stores electrical information from the second electrode pair. The negative impedance conversion circuit 570 generates a skin impedance from the electrical information stored in the impedance storage unit Mem1. That is, the impedance storage unit Mem1 temporarily holds the impedance between the second electrode pair, and the negative impedance conversion circuit 570 generates a negative impedance by inverting the positive and negative of the held impedance.

[0075] 23 is a diagram illustrating the operation of the bioelectrical impedance measuring device 500 in the modified example of the first embodiment. The bioelectrical impedance changes over time.

[0076] 8-5.Combined use of frequencies High-frequency and low-frequency currents may be passed through a living body. The low-frequency current bypasses cells and flows through the external fluid. On the other hand, the high-frequency current flows not only through the external fluid but also through the internal fluid within the cells. This makes it possible to measure changes in the ratio of the extracellular fluid resistance Rout to the intracellular fluid resistance Rin. For example, by using this ratio as an evaluation index, it is possible to evaluate the degree of muscle fatigue according to individual differences. The low frequency is, for example, 100 Hz or higher and 10 kHz or lower. The high frequency is, for example, 50 kHz or higher and 5 MHz or lower.

[0077] 8-6. Evaluation of muscle fatigue The calculation unit 190 of the measuring device 100 may evaluate the degree of fatigue of a person's arm after measuring the bioelectrical impedance. When muscles become fatigued, blood flows into the muscles. Because the conductivity of blood is higher than that of muscle, muscle fatigue tends to decrease the real part of bioelectrical impedance. During muscle exercise, a large amount of blood flows into the muscles, causing a change in their conductivity. Even if sweating occurs simultaneously with muscle exercise, the measuring device 100 can measure muscle impedance while eliminating the influence of the amount of sweating, thereby evaluating the degree of muscle fatigue. For example, the calculation unit 190 evaluates the degree of muscle fatigue from changes in the impedance of the living muscle. Alternatively, the measuring device 100 may have an evaluation unit that evaluates the degree of muscle fatigue.

[0078] 8-7.Ammeter The ammeter 150 may be disposed external to the current source 140. In this case, the ammeter 150 is connected in series with the current source 140.

[0079] 8-8. Arithmetic section The calculation section 190 may control the current source 140 .

[0080] 8-9. Combination The above modifications may be combined.

[0081] (Addendum) A bioelectrical impedance measuring device according to a first aspect includes a first pair of electrodes for contacting a living body, a second pair of electrodes for contacting the living body, a current source for passing a current between the first pair of electrodes, a voltmeter for measuring the voltage between the second pair of electrodes, a negative impedance conversion circuit connected between the voltmeter and one terminal of the second pair of electrodes, and a calculation unit. The second pair of electrodes is brought into contact with a position inside the contact position between the living body and the first pair of electrodes. The negative impedance conversion circuit generates an impedance of the skin of the living body and feeds it back to the voltmeter. The calculation unit calculates the impedance of the muscle of the living body based on the voltage of the voltmeter and the current flowing through the current source.

[0082] A second aspect of the bioelectrical impedance measuring device includes a third pair of electrodes for contacting a living body. The third pair of electrodes is brought into contact with a position inside the contact position between the living body and the first pair of electrodes. A negative impedance conversion circuit generates skin impedance based on electrical information from the third pair of electrodes.

[0083] A third aspect of the bioelectrical impedance measuring device includes a first resistor between one terminal of the second electrode pair and the voltmeter, and a second resistor between one terminal of the third electrode pair and the negative impedance conversion circuit, where the resistance value of the first resistor is different from the resistance value of the second resistor.

[0084] In the bioelectrical impedance measuring device according to the fourth aspect, one terminal of the second electrode pair has a comb-teeth shape, one terminal of the third electrode pair has a comb-teeth shape, and the comb-teeth shape of the one terminal of the second electrode pair and the comb-teeth shape of the one terminal of the third electrode pair can be arranged in an interdigitated state.

[0085] In a fifth aspect of the bioelectrical impedance measuring device, the first electrode pair has a first terminal and a second terminal. The second electrode pair has a first terminal and a second terminal. The third electrode pair has a first terminal and a second terminal. The angle formed by a line connecting the first terminal of the first electrode pair to the second terminal of the first electrode pair and a line connecting the first terminal of the second electrode pair to the second terminal of the second electrode pair is between 0° and 10°.

[0086] In a sixth aspect of the bioelectrical impedance measuring device, the first electrode pair has a first terminal and a second terminal, the second electrode pair has a first terminal and a second terminal, and the third electrode pair has a first terminal and a second terminal. The first terminal of the second electrode pair and the first terminal of the third electrode pair are adjacent to each other. The second terminal of the second electrode pair and the second terminal of the third electrode pair are adjacent to each other. The angle formed by a line connecting the first terminal of the second electrode pair and the first terminal of the third electrode pair and a line connecting the second terminal of the second electrode pair and the second terminal of the third electrode pair is between 0° and 30°.

[0087] A seventh aspect of the bioelectrical impedance measuring device includes a switch for switching on / off the connection between each terminal of the second electrode pair and each of the other components, a control unit for controlling the switch, and an impedance storage unit. The impedance storage unit stores electrical information from the second electrode pair. The negative impedance conversion circuit generates a skin impedance from the electrical information stored in the impedance storage unit. The control unit measures the impedance using the second electrode pair during a first period and causes the negative impedance conversion circuit to generate a negative impedance during a second period different from the first period.

[0088] In the bioelectrical impedance measuring device according to the eighth aspect, the calculation unit evaluates the degree of muscle fatigue from changes in muscle impedance.

[0089] In a ninth aspect of the method for measuring bioelectrical impedance, a first pair of electrodes is brought into contact with the surface of a living organism. A second pair of electrodes is brought into contact with the surface of the living organism at a position inside the contact point with the first pair of electrodes. A third pair of electrodes is brought into contact with the surface of the living organism at a position inside the contact point with the first pair of electrodes. A current is passed through the living organism via the first pair of electrodes. The voltage across the second pair of electrodes is measured. A negative impedance is generated by reversing the positive and negative of the impedance between the third pair of electrodes. The impedance of the living organism's muscles is calculated based on the negative impedance and the impedance between the second pair of electrodes.

[0090] In a tenth aspect of the method for measuring bioelectrical impedance, a first pair of electrodes is brought into contact with the surface of a living body. A second pair of electrodes is brought into contact with the surface of the living body at a position inside the contact point with the first pair of electrodes. A current is passed through the living body via the first pair of electrodes. The voltage across the second pair of electrodes is measured. The impedance between the second pair of electrodes is temporarily held, and a negative impedance is generated by inverting the positive and negative sign of the held impedance. The impedance of the living body's muscles is calculated based on the negative impedance and the impedance between the second pair of electrodes. [Explanation of symbols]

[0091] 100...Measuring device 111...1st terminal 112…Second terminal 121...1st terminal 122…Second terminal 131...1st terminal 132…Second terminal 140…Current source 160...Voltmeter 170...Negative impedance conversion circuit 190...Arithmetic section

Claims

1. a first electrode pair for contacting a living body; a second electrode pair for contacting the living body; a third electrode pair for contacting the living body; a current source that applies a current between the first electrode pair; a voltmeter for measuring the voltage between the second electrode pair; a negative impedance conversion circuit connected between the voltmeter and one terminal of the second electrode pair; A calculation unit; and The second electrode pair is The electrode pair is brought into contact with the living body at a position inside the contact position between the living body and the first electrode pair, The third electrode pair is the first electrode pair is brought into contact with the living body adjacent to the second electrode pair at a position inside the contact position between the living body and the first electrode pair; The negative impedance conversion circuit comprises: a negative impedance is generated by inverting the positive and negative of the real and imaginary parts of the impedance between the third electrode pair, and the negative impedance is fed back to the voltmeter so as to cancel the impedance of the skin of the living body; The calculation unit Calculating the impedance of the muscle of the living body based on the voltage of the voltmeter and the current flowing through the current source. A bioelectrical impedance measuring device comprising:

2. a first electrode pair for contacting a living body; a second electrode pair for contacting the living body; a current source that applies a current between the first electrode pair; a voltmeter for measuring the voltage between the second electrode pair; a negative impedance conversion circuit connected between the voltmeter and one terminal of the second electrode pair; a memory unit that stores values ​​of a real part and an imaginary part of the impedance between the second electrode pair; a switch that switches between a connection between the second electrode pair and the voltmeter and the negative impedance conversion circuit, and a connection between the second electrode pair and the storage unit; a control unit that controls switching of the switch; A calculation unit; and The second electrode pair is The electrode pair is brought into contact with the living body at a position inside the contact position between the living body and the first electrode pair, The negative impedance conversion circuit comprises: a negative impedance is generated by inverting the positive and negative of the real and imaginary parts of the impedance between the second electrode pair stored in the memory unit, and the negative impedance is fed back to the voltmeter so as to cancel out the impedance of the skin of the living body; The control unit measuring an impedance between the second electrode pair using the second electrode pair during a first period; causing the negative impedance conversion circuit to generate a negative impedance during a second period different from the first period; The calculation unit Calculating the impedance of the muscle of the living body based on the voltage of the voltmeter and the current flowing through the current source. A bioelectrical impedance measuring device comprising:

3. 2. The bioelectrical impedance measuring device according to claim 1, a first resistor between one terminal of the second electrode pair and the voltmeter; a second resistor is provided between one terminal of the third electrode pair and the negative impedance conversion circuit; The resistance value of the first resistor is different from the resistance value of the second resistor. A bioelectrical impedance measuring device comprising:

4. 4. The bioelectrical impedance measuring device according to claim 1, wherein: one terminal of the second electrode pair has a comb-teeth shape; one terminal of the third electrode pair has a comb-teeth shape; The comb-tooth shape of the one terminal of the second electrode pair and the comb-tooth shape of the one terminal of the third electrode pair can be arranged in an interdigitated state. A bioelectrical impedance measuring device comprising:

5. 4. The bioelectrical impedance measuring device according to claim 1, wherein: the first electrode pair having a first terminal and a second terminal; the second electrode pair has a first terminal and a second terminal; the third electrode pair has a first terminal and a second terminal; a straight line connecting the first terminal of the first electrode pair and the second terminal of the first electrode pair; The angle formed by the line connecting the first terminal of the second electrode pair and the second terminal of the second electrode pair is Between 0° and 10° A bioelectrical impedance measuring device comprising:

6. 4. The bioelectrical impedance measuring device according to claim 1, wherein: the first electrode pair having a first terminal and a second terminal; the second electrode pair has a first terminal and a second terminal; the third electrode pair has a first terminal and a second terminal; the first terminal of the second electrode pair and the first terminal of the third electrode pair are adjacent to each other, the second terminal of the second electrode pair and the second terminal of the third electrode pair are adjacent to each other, a straight line connecting the first terminal of the second electrode pair and the first terminal of the third electrode pair; The angle formed by a line connecting the second terminal of the second electrode pair and the second terminal of the third electrode pair is Between 0° and 30° A bioelectrical impedance measuring device comprising:

7. 7. The bioelectrical impedance measuring device according to claim 1, The calculation unit Evaluating the degree of fatigue of the muscle based on a change in the impedance of the muscle. A bioelectrical impedance measuring device comprising:

8. A first electrode pair is brought into contact with a surface of a living body; a second electrode pair is brought into contact with a surface of the living body at a position inside a contact point with the first electrode pair; a third electrode pair is brought into contact with the second electrode pair at a position on the surface of the living body that is inside a contact point with the first electrode pair, the third electrode pair being adjacent to the second electrode pair; A current is applied to the living body via the first electrode pair; measuring a voltage across the second electrode pair; generating a negative impedance by inverting the positive and negative values ​​of the real and imaginary parts of the impedance between the third electrode pair; calculating the impedance of the muscle of the living body based on the negative impedance and the impedance between the second electrode pair; A method for measuring bioelectrical impedance, comprising:

9. A first electrode pair is brought into contact with a surface of a living body; a second electrode pair is brought into contact with a surface of the living body at a position inside a contact point with the first electrode pair; A current is applied to the living body via the first electrode pair; measuring a voltage across the second electrode pair; temporarily holding the real and imaginary parts of the impedance between the second electrode pair, and inverting the positive and negative sides of the held real and imaginary parts to generate a negative impedance; calculating the impedance of the muscle of the living body based on the negative impedance and the impedance between the second electrode pair; A method for measuring bioelectrical impedance, comprising:

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